Mannose-modified hemocyanin enhances pathogen endocytosis by crustacean hemocytes.

In crustaceans, hemolymph plasma contains more than 90% hemocyanin, whereas hemocytes have minimal levels, suggesting a regulated uptake mechanism. Here, we demonstrate that in Penaeus vannamei, hemocytes internalize plasma hemocyanin under normal conditions via phagocytosis, clathrin-mediated endocytosis, and micropinocytosis. This uptake is significantly enhanced during bacterial (Vibrio parahaemolyticus, Vibrio alginolyticus, Staphylococcus aureus, Streptococcus iniae) and viral (White spot syndrome virus) infections or upon stimulation with pathogen-associated molecular patterns. While post-translational modifications (PTMs) such as dephosphorylation, deacetylation, and mannosylation enhance hemocyanin's pathogen-binding affinity, only mannosylation promotes mannose receptor-mediated endocytosis for intracellular clearance, whereas dephosphorylation and deacetylation facilitate extracellular pathogen elimination. These findings reveal that hemocyanin functions beyond oxygen transport, acting as an immune effector that undergoes PTMs to enhance intracellular pathogen clearance.